Nowadays, modern people often live in a high rise building such as an apartment or a skyscraper. In such a high rise building such as an apartment or a skyscraper, the front side (southern exposure in the northern hemisphere) facing the sun is always lighted, but the rear face (northern exposure) at the opposite side to the sun is blocked from sunlight by the shadow of the building itself, and another building at the rear side of the building experiences violation of the right-to-sunshine by the building at the front side such that sunlight cannot be transmitted even to the front face thereof. Thus, modern people who live in a place which has no window installed to face the south and in a place experiencing the violation of the right-to-sunshine by a front building, has a very high probability of catching a modern disease such as a sunlight deficiency syndrome due to deficiency in the amount of sunlight.
Accordingly, to solve this, efforts have been continued to secure an amount of sunlight by installing natural lighting devices at a high area such as a rooftop of a building. These natural lighting devices are installed on a rooftop of a high rise building such as an apartment or a skyscraper and can thus limitedly provide a portion of indoor areas with sunlight or can compensate a sunlight-unreachable portion of areas in a building for sunlight.
In order to expand sunlight transmitted to a lighting area, a reflective plate equipped with a surface formed such that sunlight is expanded or a convex mirror is used in these natural lighting devices.
However, when the reflective plate equipped with a surface formed such that sunlight is expanded is used, there is a problem in that lighting efficiency is remarkably degraded because sunlight is scattered to regions other than a lighting area while sunlight is reflected. Also, when the convex mirror is used, there is a problem in that a separate custom-made mold, which is manufactured according to a distance between the natural lighting device and the lighting area and an expansion ratio, is required. In addition, there is a common problem in that it is impossible to set the dispersion or concentration of sunlight with respect to the lighting area.